Additive manufacturing, rapid manufacturing or rapid prototyping methods for producing three-dimensional components are well known in the art (see for example U.S. Pat. No. 4,863,538—Deckard). There are various known methods of additive manufacturing including consolidation of powder materials and curing of polymeric resins (Stereolithography—SLA). SLM and SLS manufacturing methods involve a layer-by-layer consolidation of powder material using a focused energy beam, such as a laser beam or an electron beam.
In a typical selective SLS or SLM process, a thin layer of powder is deposited over a build area or powder bed within a SLS or SLM apparatus. A focused laser beam is scanned across portions of the powder layer that correspond to a cross-section of the three-dimensional article being constructed such that the powder at the points where the laser scans is consolidated either by sintering or by fusion. The cross-section is typically generated from a 3-D description of the component, which is itself generated by scanning an original component or from computer-aided design (CAD) data.
After consolidation of a layer, the build surface is lowered by the thickness of the newly consolidated layer and a further layer of powder is spread over the surface. Again, the surface is irradiated with a laser beam in portions of the layer that correspond to a cross-section of the three-dimensional article, the newly consolidated layer being joined to the initial consolidated layer. This process is repeated until the component is completed.
Typical additive manufacturing apparatuses build components onto a rigid metallic plate or substrate from which the component can be removed or, alternatively, which can be incorporated into the final component. Where component parts are removed from the rigid substrate, these parts are generally removed by mechanical means such as filing, sawing, milling, spark discharge etc. Such removal processes are time-consuming, expensive and need to be performed carefully so as not to damage finished parts. In addition, the rigid metallic substrate needs to be refurbished after each use before it can be used for another build. Such refurbishment is typically carried out by milling the substrate flat. Thus, a layer of the substrate is typically lost every time it is used and such substrates are, therefore, a consumable item.
The rigid substrate must be made of a material to which the build material (i.e. the material used to build the desired component) will weld or adhere during processing. Very often the substrate needs to be of a similar material or the same material as the build material. Such consumable build plates can be extremely expensive. For example, a titanium build plate for use in a selective laser melting apparatus having dimensions of 250 mm by 250 mm can cost in excess of £1000. The accumulated cost of machining removal of components, refurbishment of the build plate, and the gradual loss of the build plate through erosion can add a significant amount to the cost of individual components produced by the additive manufacturing process.
Ideally, components could be built on the free powder bed, i.e. built without being constrained to a build substrate. This is not usually possible with additive manufacturing processes such as SLM and SLS as there are high thermal stresses generated in parts as they are produced. Distortion during deposition of the initial layers of the component could severely affect the integrity of the finished component. Electron beam manufacturing process such as E-Beam melting (EBM) or E-Beam sintering (EBS) are similar processes to SLM and SLS. EBM often utilises a higher build temperature than SLM and this means that the thermal stresses in the components can be lower. Thus, EBM allows, in some circumstances, the production of self supporting components that do not need to be bonded or adhered to a substrate. It is, however, sometimes desirable or necessary to anchor a part when using EBM and in such cases anchoring is done in similar ways as described above for SLM processes.
A typical prior art apparatus is disclosed by U.S. Pat. No. 5,753,274. This US patent describes an apparatus for producing a three-dimensional object by solidification of successive layers of a powder material, the apparatus including a rigid base plate made from a material to which the powder adheres when being solidified and means for removably connecting the base plate to support means in the apparatus.